The arctic ocean becomes like the atlantic ocean

On a cold morning toward the end of July, the research vessel Oceania, a blue-and-white three-master, steers through the dark waters of a fjord on the west coast of the Arctic island of Spitsbergen. Rugged peaks covered in snow streaks rise steeply from the water. Vast streams of glacial ice plow up the mountains and flow into the fjord, where they drop abruptly to towering turquoise walls. Chunks of ice, crackling and popping like bubble wrap, drift by as they melt to release the air already held inside them some time ago.

As the ship drops anchor, scientists dressed in wool sweaters, knitted caps, rubber boots and thickly lined sailor jackets stream onto deck and begin their work. One of the researchers launches a silver box-like device to record temperature, salinity and depth of water. Another spreads a funnel-shaped net on the seabed at the side of the ship with the help of a winch. As it pulls up, a veritable menagerie of tiny sea creatures gathers in the fine-meshed fabric, among them krill, copepods or copepods, other small crustaceans and some jellyfish the size of grapes.

This article is featured in Spectrum – The Week, 08/2018

Although the tiny, transparent copepods with their thin, red antennae are among the most unsightly objects of the treasure that the researchers have recovered from the sea, they are nevertheless the focus of general attention. "We want to find out who they are, where they live and how many of them there are", explains marine ecologist Sławomir Kwaśniewski, who works at the Institute of Oceanography of the Polish Academy of Sciences (IO PAN) in Sopot, Poland. The microscopic crustaceans represent the crucial middle link in the condensed food web of the Arctic: They are the most important food source for polar cod, seabirds and bowhead whales, and their energy and nutrient content ultimately contributes to the diets of seals, reindeer and polar bears as well. By looking more closely at copepods and the Arctic ecosystem they sustain – from the seafloor to the rocky cliffs densely populated by birds – scientists hope to better understand the ways in which climate change is currently restructuring the Arctic food web and altering the overall biological character of this habitat.

The Arctic is atlanticizing

Scientists’ interest in the small copepods is largely due to a phenomenon that has only been observed relatively recently – the so-called atlantification of the Arctic. After many years of sampling, researchers have found that the Arctic Ocean is losing its typical Arctic characteristics and becoming increasingly like the Atlantic Ocean; its ice is melting and its water temperatures are rising. As a result, animals from warmer climates are invading Arctic waters and causing massive changes to natural biodiversity there. A single copepod species is just now providing the first clues to the extent of this disturbance and its potential consequences.

For more than a century, marine scientists have known that water masses from the Atlantic Ocean flow past Europe, squeeze between Greenland and the Norwegian island of Spitsbergen, and eventually flow into the Arctic Ocean in an offshoot of the Gulf Stream, the West Spitsbergen Current. Atlantic water is warmer and saltier than Arctic Ocean water, which has both cooler temperatures and lower salinity due to melting sea ice, calving glaciers, and freshwater inflow from the mighty rivers of Siberia and Canada. In other oceans, cold water is generally heavier and therefore remains near the bottom of the sea. In the Arctic Ocean, however, the lower salinity and the lower density of the cooler water cause a reversal of the conditions, so that here the warmer Atlantic water flows along the seabed.

By measuring temperature and salinity at different depths, scientists can precisely locate the course of these water masses. When a researcher lowers a measuring probe in the waters above the continental shelf near the west coast of Spitsbergen, the largest island in the Norwegian archipelago of the same name, the device first passes through cold water with comparatively low salinity on its way to the depths. At some point, it hits the halocline, a layer of cold but increasingly salty water, and eventually reaches a third layer of water, the warmer, more saline Atlantic water. The halocline prevents mixing of warm and cold water masses and ensures that the different layers remain intact.

However, the warming earth and melting sea ice are currently upsetting these three water layers. The West Spitsbergen Current is now transporting a greater volume of much warmer Atlantic water into the Arctic Ocean, rising air temperatures are heating the upper water layer, and because of the lack of sea ice cover, whipping winds are causing the surface water to foam. All of these processes cause a weakening of the halocline and allow mixing of the once separate water layers. In some regions of the Arctic, scientists have detected warm water masses even close to the sea surface, so the Atlantic is appearing in places where it has never been observed before.

Atlantic water masses at shallow depths

In the past, the fjords located on the west coast of Spitsbergen were spared from the inflow of Atlantic water. The strong halocline of the fjord waters prevented the influx of warm, salty water masses, and the inlets themselves were sufficiently shallow that their entrances in the cold-water zone were well above the reach of Atlantic water. Over the last ten years, however, Atlantic water masses have increasingly made their way into shallower water depths and have already penetrated numerous fjords. This not only makes these inlets warmer and saltier, but also provides more favorable living conditions for the tiny creatures that drift in with the currents.

"In the past, a beautiful sheet of ice used to form on Arctic waters, and deep below it flowed the Atlantic water, but no one cared because it was at such a great depth", reports Jan Marcin Węsławski, head of the Ecology Department at IO PAN. But a lot has changed since he started exploring this Arctic region. "The ice has disappeared, and we find the warm water once hidden all the way to the shores of Spitsbergen", is how the scientist describes the situation today.

In the long fjord near Longyearbyen, the largest city on Spitsbergen, the influx of warm water has led to profound changes. "In the past, the ice on the fjord was more than 90 centimeters thick in winter", Kim Holmen, the international director of the Norwegian Polar Institute, notes. "Now the whole darn thing hasn’t frozen over in seven years." In January 2017, when air temperatures dropped to minus 21 degrees Celsius, the weather in Longyearbyen may have felt quite frigid, but with water temperatures ranging from 2.8 to 3.8 degrees Celsius, the fjord was not covered by a layer of ice even that winter. The lack of sea ice does prevent the village’s 2,000 or so residents from riding their snowmobiles to recreational camps and log cabins on the other side of the fjord, as they had been accustomed to doing for many decades. On the other hand, people can now catch Atlantic cod in these waters (Gadus morhua) catch.

Another fjord, whose waters are also warming, has been studied particularly thoroughly: Kongsfjord, located about 100 kilometers north of Longyearbyen, on whose shore the research village of Ny-Ålesund is situated. In the winter of 2005/2006, scientists observed an influx of Atlantic water there for the first time. Since then, little solid ice has been sighted on the inlet that was once covered by ice every winter. But not all fjords on the west coast of Spitsbergen have changed in this way. Hornsund, located about 139 kilometers south of Longyearbyen, has been able to retain its typical Arctic characteristics and thus provided Węsławski and his colleagues with a perfect opportunity for comparative water analyses. The researchers began to document the changes in natural conditions in the other fjords of Spitsbergen so that they could subsequently compare them with Hornsund. "This is a natural experiment – like studying two aquariums", clarifies the scientist.

As part of this experiment, 14 scientists spent a three-week research stay on the Oceania on the west coast of Spitsbergen in summer 2017. The ship zigzagged along the West Spitsbergen shelf and entered various fjords, including Kongsfjord and Hornsund. Researchers stopped every few hours to take samples of water, mud and marine organisms and to assess the overall health of the Arctic Ocean in the area.

Back on board the Oceania, in the ship’s laboratory near the aft deck, Kwaśniewski pours some of the sample caught with the zooplankton net into a beaker and places it on a box under a light source to get a closer look at the tiny creatures. The copepods, which are about the size of red garden ants, move back and forth in the water. It seems to be mainly Calanus glacialis a copepod common in cold, Arctic waters, but only after a detailed microscopic examination in his laboratory in Poland can Kwaśniewski be really sure of it.

C. glacialis, sometimes referred to as "the Arctic copepod" forms a central part of the Arctic food web and, according to many scientists, represents the most important species of the entire ecosystem. But recently, the copepod has also been the focus of some new and very disturbing developments.

Compared to low-latitude habitats, Arctic habitats are characterized by lower biodiversity because far fewer organisms can thrive in conditions that are too cold or too dark for most temperate species. While the North Atlantic can boast some 20,000 species, the Arctic Ocean waters around the Spitsbergen archipelago are home to only 2,500; some of these species are not found in any other world ocean.

Biodiversity on the rise

In many areas of the world, the ecological effects of climate change are often accompanied by a loss of biodiversity. But in the fragile Arctic ecosystem, this effect is reversing: instead of losing species, the Arctic is gaining new ones, and these immigrants are not only surviving there, but multiplying rapidly. "The natives are still there, but they are quite soon eclipsed by the newcomers", states Węsławski. Thus, as Atlantic waters continue to penetrate the fjords of West Spitsbergen, species more normally found in subarctic and boreal regions are entering this marine area, including the copepod Calanus finmarchicus. Even if both species of copepods appear almost identical to the untrained eye, however C. finmarchicus, often referred to as "the boreal copepod" is smaller in size and contains about ten times less energy than its fatty, Arctic cousin C. glacialis.

Based on data collected in recent years, researchers have concluded that the changes described above are already underway at Kongsfjorden. The water in this estuary is now on average one degree Celsius warmer than in Hornsund, and as a result zooplankton species that are rarely found in Hornsund are abundant there. Significantly, over the past decade, the boreal-originating C. finmarchicus has almost always been much more prevalent than its Arctic relative C. glacialis. Despite occasional fluctuations in abundance, made C. finmarchicus In 2014, more than 96 percent of all species present in water samples from Kongsfjorden were present in terms of quantity.

These shifts in species composition may be almost imperceptible at first, and seem relatively insignificant, until at some point they can no longer be ignored. The blue mussel (Mytilus edulis), which disappeared from the coasts of the Spitsbergen archipelago about 1000 years ago during a period of climate cooling, has reestablished itself in the Kongsfjord in the past decade as its larvae have been transported to the area by warm currents from the North Atlantic. Also the mackerel (Scomber scombrus) has appeared in large numbers in the fjord waters, which in turn has contributed to a population of gannets there (Morus bassanus) could establish itself. But far more troubling is the change in the species range of copepods in favor of the smaller species native to southern waters. This change could become a serious problem for predators living in the Arctic, among them the common shrike (All all), a bird that nests in the millions on the island of Spitsbergen and relies on the energy-rich Arctic copepods as a food source.

Typical species of the Arctic are being displaced

"The more the Arctic system is disturbed by Atlantic influence, the more difficult life becomes for typical species of the Arctic, such as the crab diver", states Kwaśniewski. "These animals come here deliberately. They breed in this area because they know that the waters hold an abundant supply of prime food for them. And this food is directly related to the Arctic marine environment."

After sampling is complete, the scientists stow their nets and retire to the ship’s laboratory. The Oceania’s engine comes noisily to life, and the ship moves away from the glacier tongue toward the mouth of the fjord to head for the next sampling station. Polish pop music pours through the open door of the onboard lab, where a half-dozen students are busy filtering water samples, sorting zooplankton catches and preparing for the next measurements. The swell is getting stronger as we pass countless, almost motionless crab divers with their characteristic anvil-shaped heads and bulging cheeks. One of the birds emerges from the water right next to the ship and frantically flaps its wings to take to the air. But instead, it skips across the surface of the water like a flat stone, weighed down by the weight of the meal it has just eaten.

The Polish polar station is located on a coastal terrace at Hornsund just above the fjord mouth. The building was constructed in the mid-1950s and has since been inhabited, abandoned, recommissioned, rebuilt, expanded, and finally transformed into a modern research station that now hosts scientists year-round. Photographs of days gone by, featuring hibernating explorers in their finest ceremonial attire and curious polar bears peering in through the kitchen window, adorn the pine-paneled walls. On the steep embankment behind the station is one of the largest colonies of crab divers in the archipelago. Countless of the small, black and white birds nest there in the rocky cliffs. Every spring, more than a million breeding pairs settle on the Spitsbergen archipelago; about 400,000 of these bird pairs build their nests on the Hornsund.

Daily monitoring of the breeding colony

Katarzyna Wojczulanis-Jakubas, an ornithologist from Poland’s University of Gdansk, picks her way across the tundra to the hillside bird colony. Carefully, the researcher, equipped with knee pads and a binocular harness, wears her long, dark hair in a knot looped at the nape of her neck, and walks past reindeer excrement and tufts of fur. As it continues its ascent, it is careful not to step on loose rock so as not to destroy any of the nests located near the bottom. Higher up, clouds streak the tops of the mountains.

During the summer months, Wojczulanis-Jakubas and her colleagues check the breeding colony daily. Some days they catch a few birds to take various body measurements on them and take samples of recently caught prey. Today, however, the scientists’ main focus is on the camera traps they had set up in the colony to monitor the birds’ parents’ comings and goings between nests and feeding grounds, which they now plan to reset. The closer we get to the crab diver colony, the louder the shrill chattering of the animals reaches us. The smell of her guano also intensifies – smoky and sour, like burning peat. At a pile of rocks piled on top of each other, marked by a short stick wrapped in orange tape, Wojczulanis-Jakubas makes a stop. The ornithologist rolls up her sleeves, reaches into an opening and pulls out a week-old chick covered in black down. Its parents are probably out at sea catching food, the scientist explains.

Crab divers are attracted to them because of the fatty, arctic copepods C. glacialis to the Hornsund. This copepod provides the birds with the energy they need to raise their offspring during the summer and then make the approximately 1930-kilometer journey to their wintering grounds off the south coast of Greenland. Of the various copepod species, crab divers prefer to eat the large, high-energy C. glacialis. In a small pocket of their gullet called the throat pouch, adult birds can store hundreds of these crustaceans and transport them to their young.

Crab divers selectively feed on

For more than twelve years, Katarzyna Wojczulanis-Jakubas and her husband Dariusz Jakubas have spent nearly every summer on Spitsbergen studying these small, squat seabirds. About a decade ago, the two biologists were members of a research team studying the feeding habits of crab divers. The scientists captured birds returning from foraging and, using a small spoon, took food samples from their throat pouches. It turns out that the seabirds selectively eat C. glacialis transported to their nests. The copepod accounted for 80 percent of the prey caught by the crab divers, although its share of the zooplankton in the feeding grounds was only about 10 to 15 percent. Although the birds can eat both Calanus-species "but they know that C. glacialis is the best.", Jakubas, who also works at the University of Gdansk, emphasizes.

Just as fish and zooplankton are susceptible to changes in salinity and water temperature, crabeater grebes may also prove sensitive in this regard. For example, many scientists who study these seabirds more closely have doubts about whether crab diver chicks feed exclusively on C. finmarchicus They were able to feed the birds without having another, calorie-rich food source available to them. So a massive change in the abundance of their key food organisms could have catastrophic consequences for the crabeater colony, while also having the potential to completely transform the terrestrial ecosystem surrounding the birds.

Towards the end of the 19. At the beginning of the 20th century and with the end of the Little Ice Age, the Little Grebe left its former breeding grounds in the south of Greenland and Iceland. One hypothesis attributes this phenomenon to a change in water conditions around the bird colonies. Rising temperatures caused a shift in ocean currents near Greenland and Iceland, which then carried warmer water near the crab diver colonies. Some scientists postulated that the birds either moved away or became extinct because they no longer had access to their preferred prey organisms.

Crab divers lose their food base?

To test whether the current influx of warm Atlantic water into the fjords of Spitsbergen is having an effect on the Common Loons, ornithologists have monitored two spatially separated bird colonies. In 2011, Hornsund-dwelling shearwaters and conspecifics from a colony on Magdalenefjord – a warm-water fjord in far northwestern Spitsbergen – were fitted with GPS loggers on their backs. Using data records, the researchers determined that crab divers traveled further from Magdalenefjord and flew beyond warm-water areas to the edge of the Arctic sea ice zone, where they presumably C. glacialis found. However, such a picky feeding behavior also had its price. These birds spent a longer time in the air and accordingly expended more energy than their conspecifics that preyed on food near Hornsund. For example, a shearwater from the Magdalenefjord colony flew 150 kilometers to forage at the ice edge, while none of the birds living in the Hornsund covered flight distances of more than 61 kilometers.

Other scientists found that crab divers foraging in warm-water conditions had higher concentrations of the stress hormone corticosterone in their blood. According to a study conducted toward the end of the breeding season, the weight of these adult birds was significantly lower, and a smaller proportion of them survived the following months of the post-breeding season. Wojczulanis-Jakubas, on the other hand, has so far not been able to detect any obvious damage, either to the bird parents she studied or to the young shearwaters. However, the ornithologist believes that there is a limit – a threshold at which birds are no longer able to counteract. "It will show up in body weight and perhaps colony size", speculates the researcher.

Perched on the scree-covered slope, Wojczulanis-Jakubas points to the bright patches of vegetation below that adorn the lower section of the hill like a chunky emerald necklace. Vast tundra meadows, colored in a mixture of light green and yellow, extend to the shore. By Arctic standards, they represent lush oases, a buffet for Svalbard reindeer, Arctic foxes, Eastern European field mice and white-cheeked geese. "This is an ornithocoprophile tundra", explains the biologist with a laugh "a tundra that loves bird droppings. And at the very beginning are the crab divers."

Bird droppings as the basis for the ecosystem

The birds have given rise to this terrestrial ecosystem of the Arctic and created a link between the sea and the land. Their feces are rich in nitrogen, an essential nutrient for mosses, lichens and dwarf willows, which in turn feed the mammals of the Svalbard archipelago. If you look through binoculars to the other side of the fjord, all you see are lifeless, gray rocks without a single bird. "There is practically nothing over there", Wojczulanis-Jakubas notes. In the terrain that stretches on our side between the bird colony and the coast, 100 percent of the nitrogen contained in the plants comes from the excrement of the crab divers.

It is still too early to make predictions about the future of the Hornsund bird colony or other Svalbard shearwater populations. However, there is evidence that climate change and a shift in the copepod species range in favor of the less nutritious boreal species could spell the final end for these birds. The peculiarity of the crabeater to visit the same breeding area every year would make it difficult to relocate the birds if the situation in their feeding grounds deteriorates further. Other researchers have already noted a link between warmer climate conditions on Spitsbergen and lower survival rates of adult crabeater divers, and suggest that the influx of copepods from boreal zones may be to blame for this development.

If the shearwaters do indeed disappear from Svalbard or dramatically decrease in numbers, it could result in the transformation of a landscape that is vital to the survival of herbivores like reindeer. While other seabirds might occupy the niche left by the crabeater divers; nevertheless, the loss of one tiny copepod could fundamentally change the unique biological character of this island.

Warm waters in the innermost estuary

Above our heads, a lone glaucous gull soars (Larus hyperboreus) lazily make their slow circles in the sky, sending thousands of crabeater divers into wild turmoil. Even after the birds have landed, the air is still filled with their loud warning trills and frantic wing beats. Meanwhile, aboard the Oceania, Kwaśniewski comes up with disturbing news about Hornsund – the fjord that scientists had previously used as a reference area for Arctic conditions. Four years ago, the research team had detected Atlantic water there for the first time; today, however, they were able to detect the warm water masses up to the innermost parts of the estuary. "Now, of course, we wonder if the Atlantic zooplankton was also transported this far into Hornsund", reflects Kwaśniewski.

Two days later we leave the fjord late in the evening and sail towards the southern tip of the island. Heavy swells cause the boat to sway more than before. The next morning we are no longer between snow-covered mountains, but look at them from the open water, while we drift over the edge of the continental shelf. The water also looks very different here; its color has changed from the milky gray-brown of glacial meltwater to a clear, dark turquoise. As the winds drop the funnel-shaped plankton net into the sea, we can still see its white glow down to depths of more than 20 meters.

Under the relentless midnight sun, our ship zigzags north along the Spitsbergen coast for the next few days. Kwaśniewski divided the scientific crew into two shifts: While the first takes zooplankton samples on deck and conducts temperature and salinity measurements, the second is busy sleeping, eating or showering. Every eight hours there is a shift change. The ship interrupts its journey after every 15 kilometers to carry out the measurements. On the first day and at the first stations, the data on temperature, salinity and zooplankton composition still seem to be in line with Kwaśniewski’s expectations. The upper layers contain cold, less salty water, while the warmer, more saline water is at greater depths. We flush copepods from the plankton net and transfer them to small sample vials. As expected, it seems to be C. glacialis to act.

Ribbed jellyfish have never been seen this far north before

During its transport to more northerly regions, the Atlantic water gives off heat. It has always done this, but now the water carries much more warmth and penetrates much further north into the fjords. And late on that first day of investigation, when the ship is anchored some distance from the coast, strange readings suddenly appear. First, at a depth of 300 meters – that is, in the area of the presumed upper limit of Atlantic water – the scientists suddenly encounter very warm water, the temperature of which is five degrees Celsius. "This is the heat that is coming into the Arctic", Kwaśniewski notes as he tracks the changes in water temperature and salinity in real time on his computer. "No wonder the sea ice is melting." Then the researchers discover a ribbed jellyfish, actually a resident of warmer waters, in the zooplankton net. It is a species that has never been sighted this far north before.

At 20 to three in the morning, as our salt-encrusted rubber boots glisten in the sun after nearly 48 hours of sampling, the Oceania finally stops at the last sampling station located in the open ocean before we sail back into Hornsund. Kwaśniewski operates the winch to haul in the zooplankton net. As the fishing gear dangles above the water, I grab the ropes and pull it over the railing onto the wooden deck of the ship. Carefully I detach the blue collection container from the net and place it in a refrigerated container the size of a lunchbox. The tank is teeming with creatures – like dancing water striders on the surface of a lake. Kwaśniewski brings the cooler to the lab, pours the sample into a beaker and places it under a light source.

At this moment the scientist observes something unusual. The sample is rich in smaller copepods, which are most likely the warm-water-loving species C. finmarchicus Acts. But something is not right. Kwaśniewski grabs the camera, takes a photo and enlarges it on the computer. The copepods on the screen are not transparent, as they should be, but glow a striking red from head to toe – like the shell of a cooked lobster.

Kwaśniewski suspects the coloring is from an infection with a parasite, but it remains to be seen whether studies in his lab in Poland will confirm this, the researcher said. In the meantime, he begins to speculate what the discovery of a parasite might mean and what the possible consequences might be. "If this is a mass infection, it could pose a new problem for the Arctic system." As this stage of the research cruise is finished, we will return to Longyearbyen the same night. Once in port, some members of the scientific crew leave the ship and go home, while a new group of researchers and students succeed them. In the coming days, the Oceania will continue sailing north to continue sampling at Kongsfjorden.

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